Advice on CV for OPES Simulations of Water Clusters

[Saeed Pourasad]

Dear Gareth,

I hope you’re doing well.
I am interested in studying the behavior of small water clusters using OPES and an appropriate collective variable. You used the RDF and ADF as collective variables in your paper (J. Chem. Phys. 135, 114109, 2011).

Given that my system consists of water clusters ranging from N = 10 to 100 molecules, I would greatly appreciate your insights on whether a hydrogen bond-related collective variable (https://www.plumed.org/doc-v2.10/user-doc/html/_h_b_o_n_d__m_a_t_r_i_x.html)  might be more suitable than ADF for capturing the relevant physics.

Thank you for your time and consideration.
Best,
Saeed.

[Gareth Tribello]

Hello Saeed

I am not sure of the answer to your question.  It depends what you want to do.  In the paper you cite, we wanted to explore the free energy surface for the cluster in an unbiased way.  In other words, we wanted to build up a picture of the configurations that the cluster could adopt without using what was already known about the physics of the cluster.  Perhaps the number of hydrogen bonds that each oxygen is participating in is a good high dimensional CV.  

I think that if you want to study the transition between one cluster geometry and another then you are best off using some linear combination of some CVs that describe the geometry of the two CVs.   I would then use an idea something like the one in this paper:

To build a CV that can discriminate the configurations.

I hope this helps

Gareth   

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[Saeed Pourasad]

Thanks a lot!